1. Field of the Invention
The present invention relates generally to centrifugal force operated hydraulic governors and relates more particularly to such governors incorporated into automotive automatic transmissions for providing a pressure signal varying with vehicle speed for effecting automatic selection of gear ratios.
2. Description of the Prior Art
Vehicle automatic transmissions generally employ hydraulically operated brakes and clutches for effecting automatic selection of two or more gear ratios. This automatic selection is in part dependent on vehicle speed. To provide a hydraulic signal indicative of vehicle speed centrifugal force operated hydraulic governors are generally employed.
Certain of such governors in widespread current use utilize sliding valve members carried for rotation with a portion of the transmission which move to positions operative to vary governor output pressure in response to changes in vehicle speed. Applicant's governor shown in U.S. Pat. No. 4,194,520 and assigned to the assignee of the present invention is exemplary of such governors. While these governors have proven to be effective and reliable in operation, they are limited in accuracy and predictability of output pressure because of variations in response of individual sliding valve members to changes in centrifugal force due to tolerance build-up.
Other governors, such as that disclosed in U.S. Pat. No. 3,559,667, have enhanced accuracy by use of a flyweight type mechanism to actuate their valving elements. To achieve this accuracy, however, extremely close tolerances on the thickness of the flyweight structure pivotally mounted on the transmission rotated element of the governor must be held. This requires cost and complication that is considered impractical for the large volume production experienced in vehicle automatic transmission manufacturing.